Fix CVE-2018-0732:

https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2018-0732

Patch copied from upstream source repository:

https://github.com/openssl/openssl/commit/3984ef0b72831da8b3ece4745cac4f8575b19098

From 3984ef0b72831da8b3ece4745cac4f8575b19098 Mon Sep 17 00:00:00 2001
From: Guido Vranken <guidovranken@gmail.com>
Date: Mon, 11 Jun 2018 19:38:54 +0200
Subject: [PATCH] Reject excessively large primes in DH key generation.

CVE-2018-0732

Signed-off-by: Guido Vranken <guidovranken@gmail.com>

(cherry picked from commit 91f7361f47b082ae61ffe1a7b17bb2adf213c7fe)

Reviewed-by: Tim Hudson <tjh@openssl.org>
Reviewed-by: Matt Caswell <matt@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/6457)
---
 crypto/dh/dh_key.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/crypto/dh/dh_key.c b/crypto/dh/dh_key.c
index 387558f146..f235e0d682 100644
--- a/crypto/dh/dh_key.c
+++ b/crypto/dh/dh_key.c
@@ -130,10 +130,15 @@ static int generate_key(DH *dh)
     int ok = 0;
     int generate_new_key = 0;
     unsigned l;
-    BN_CTX *ctx;
+    BN_CTX *ctx = NULL;
     BN_MONT_CTX *mont = NULL;
     BIGNUM *pub_key = NULL, *priv_key = NULL;
 
+    if (BN_num_bits(dh->p) > OPENSSL_DH_MAX_MODULUS_BITS) {
+        DHerr(DH_F_GENERATE_KEY, DH_R_MODULUS_TOO_LARGE);
+        return 0;
+    }
+
     ctx = BN_CTX_new();
     if (ctx == NULL)
         goto err;
-- 
2.17.1

